My cat has runny eyes

Leeland is around 9 months old. I have had him 1 month. He is a rescue cat. I took him to the vet last week because his eyes are always runny and he rubs them a lot. I was told not to worry but this problem is obviously bothering Leeland. He rubs his eyes all day. Please give me any helpful advice. I love him and want him to be healthy.